Sunday, June 3, 2012

- As I said in other posts, Burrow.NET aims to generic needs of any .NET projects that use RabbitMQ. I believe the built-in code has covered most of your requirements for common usages. However there are some things you can easily change without writing any new code or at least just a few lines of code. So in this post, I'll introduce about things you can make to suit your needs when working with RabbitMQ using Burrow.NET.

1/ Global.DefaultConsumerBatchSize

- The default value of this static property is 256. When you use ITunnel object to asynchronously subscribe to a queue, Burrow.NET use a internal Semaphore object when creating asynchronous Task to handle the messages from the queue. The amount of Tasks it create will depend on this value since it's used as the initialize value for the internal Semaphore. In the mean time, this value is also used to call IModel.BasicQos, which eventually sets the maximum amount of messages stay on the Unacknowledged list when they are consumed. That's the fetchsize value mentioned in RabbitMQ document and they advise to keep this number as high as double to the acknowledge speed. Therefore, you potentially should adjust this number to fit your need. Moreover, the amount of Tasks and eventualy Threads Burrow.NET create when consumming messages is in proportion to this value and I personally think creating more threads does not make the application run faster. I'll keep monitoring the way it works in my projects so I could split the value for the queue fetch size and the number of concurrent Tasks if it's neccessary but I think so far so good.

2/ Global.DefaultPersistentMode

- This value is equal to true by default and is used when creating the ITunnel object. It's eventually used when you publish messages. If the persistent mode is true, the message will be written to disk instead of being kept in memory. So if there is any problem with the server and you have the machine reboot, your messages will be safe. Otherwise, they will be removed when server reboots. However, keeping messages in memory could improve the performance. The DefaultPersistentMode is used to create ITunnel object in TunnelFactory, but you can change it anytime as the ITunnel has a method to do that.

3/ Global.DefaultErrorExchangeName and Global.DefaultErrorQueueName

- The built-in error handler will publish any unhandled exception wrapped in an object and publish to these exchange/queue so you can modify this value to route the error messages to their new home. The default value for the exchange is "Burrow.Exchange.Error" and "Burrow.Queue.Error" for the queue.

4/ Global.DefaultSerializer

- This property hold the default value of an JavaScriptSerializer which is quite slow in performance and cannot handle serialization very well. The reason to have this is to reduce the dependencies to 3rd libraries so you can just use Burrow.dll without Burrow.Extras.dll. However, I know everyone likes Json.NET include me so there is another implementation of ISerializer locates in Burrow.Extras package using Json.NET. It's not the fastest .NET serializer but fast enough for common usages. So I strongly recommend using this one in your project. Again, this value is used to create ITunnel and the ITunnel object will have a method to change that anytime.

5/ Global.DefaultWatcher

- This one is used to write debug messages from Burrow.NET. The default value is ConsoleWatcher which writes messages to console so if you're writing a console app, you will easily see those messages. You properly want to change it to anything else such as Log4Net. To do that, simply implement IRabbitWatcher using Log4net and change the DefaultWatcher when app start.

Global.DefaultWatcher = new Log4NetRabbitWatcher();

6/ Global.DefaultCorrelationIdGenerator

- This one is used to generate the CorrelationId when you publish a message. The default implementation will generate a Guid and I think it's pretty enough for an Id. You don't have to change that but just do it if you have time and good reason

7/ Global.DefaultTypeNameSerializer

- Like the CorrelationId, this one is used to generate a string to determine the message when you publish messsags to RabbitMQ. I can think of a case we might need this value is when you just publish any type of message to the queue. When consuming the messages, base on this value you can know the type and deserialie the object. But honestly I've never tried this, neither used this value so if you don't need it in your project, leave it.

- In conclusion, I put these things in the Global class just to make it's easier to change the behavior of the ITunnel without touching to the TunnelFactory or calling methods on ITunnel object. Things like DefaultWatcher, DefaultTypeNameSerializer and DefaultCorrelationIdGenerator are the bare minimum needs for Burrow.NET and you can simply use the library without worrying about those values. Again, the only thing I suggest to take care of is the DefaultSerializer, just change it to JsonSerializer for better performance.